In recent years, a plurality of wireless communication systems is loaded on information devices to be mounted on movable bodies, typically car navigation systems. The wireless communication systems are used for a variety of applications. For example, a wireless communication system of Bluetooth is used for hands free calls, dial-up connection, and music replay between terminals, e.g., cell phones and audio players. Communication of various kinds of information is performed by wireless LAN communication systems such as IEEE802.11b/g with terminals such as personal computers and smart phones or with external access points for use in navigation and various applications.
Those Bluetooth wireless communication system and wireless LAN communication system such as IEEE802.11b/g use the same frequency band of 2.4 GHz band. Therefore, if those wireless communication systems are used simultaneously in the same area, such as an interior of a mobile object, radio interference may occur. As a result, communication quality of the both wireless communication systems may deteriorate due to the interference between them.
With the recent prevalence of wireless LAN, wireless LAN is widely used also outside the mobile object. Therefore, radio interference from other wireless LAN networks, such as an external access point and an adjacent vehicle, are also considerable. In this case, radio interference among wireless LAN networks may occur depending on a frequency allocation, as well as the interference between the wireless LAN network and the Bluetooth system.
As a method of solve the foregoing issues, Patent Literature 1 discloses an vehicle-mounted communication device. The disclosed device is configured to predict occurrence of wireless communication between a base station and the external vehicle-mounted communication device before starting wireless communication between a mobile terminal and the vehicle-mounted communication device. The disclosed device is further configured to restrict use of frequencies that may cause radio interference, and start wireless communication between the mobile terminal and the vehicle-mounted communication device by using available frequencies.